Advanced structural characterisation of agar-based hydrogels: Rheological and small angle scattering studies

Area of Science:

• Marine biotechnology
• Polymer science
• Food science

Background:

• Agar, a polysaccharide from red algae like Gelidium sesquipedale, is widely used as a gelling agent.
• Extraction methods significantly influence agar yield, purity, molecular weight, and subsequent hydrogel properties.
• Understanding the relationship between extraction conditions and hydrogel formation is crucial for optimizing agar applications.

Purpose of the Study:

• To investigate the effects of different extraction methods (heat, heat-sonication, alkali pre-treatment) on agar properties from Gelidium sesquipedale.
• To characterize the structural and rheological properties of the extracted agar.
• To elucidate the gelation mechanism and its dependence on agar characteristics.

Main Methods:

• Extraction of agar using heat, heat-sonication, and alkali pre-treatment.
• Rheological measurements to assess gel strength and mechanical properties.
• Small-angle scattering techniques to analyze molecular arrangements.
• Characterization of agar content and molecular weight.

Main Results:

• Alkali pre-treatment increased agar content but led to partial degradation and reduced molecular weight.
• Sonication resulted in lower agar content and decreased molecular weights.
• Hydrogel formation involved agarose chain association into double helices and bundles, influenced by agar purity and molecular weight.
• The mechanical performance of hydrogels varied with molecular arrangements.

Conclusions:

• Extraction methods critically influence agar yield, molecular weight, and purity, thereby affecting hydrogel properties.
• The proposed gelation mechanism highlights the role of agarose chain association in hydrogel formation and mechanical strength.
• The study indicates that the gelation process is not fully reversible, with implications for agar-based material design.